In those miserable, wonderful days when love is new, when your heart pounds and your breath comes short and sharp, the only thing that matters is your beloved. News of the outside world comes as a rumor. Daily life is a melodrama, a musical, a rom-com, an epic.This is a story of two men in the early phase of romantic love. It begins with Evan Garland, 24, who lives in Los Angeles and works in finance and accounting for the media streaming service Hulu.

On June 2, Mr. Garland stared at his smartphone screen, flipping through the dating app Tinder for what he supposed would be the last time. In roughly 400 dates, he had not come close to anything resembling true love.

He hadn’t been on a date in over a month, and none of his friends were in long-term relationships. After years of dating, Mr. Garland felt his heart had grown cold.“If one thing is wrong with someone on a date,” he said, “your mind-set is, ‘O.K., I can just swipe right and find someone new.’”

He was on the verge of deleting Tinder when he matched with a dance instructor, Diego Gasca, also 24. Mr. Garland and Mr. Gasca started texting each other and soon fell into a bantering dispute over who was better: Beyoncé or Madonna.

As more texts came rapid-fire, they realized they shared a love for horror movies, “Parks and Recreation” and “Will & Grace.”

On June 4, in the hours before their first in-person encounter, Mr. Garland realized he was nervous. By the time Mr. Gasca arrived at his apartment in West Hollywood, Calif., Mr. Garland was in free fall.

Before they set out for the night, they talked. About important things. About trivial things. About everything. About nothing. Somehow the conversation lasted two hours.They went dancing at Bootie LA, a club in the Echo Park section of Los Angeles, till well after midnight. After, Mr. Gasca spent the night at Mr. Garland’s place.

In the morning, they talked for another four hours. And when it was time for Mr. Gasca to go, neither wanted to part. Mr. Garland was still in the thrall of intense emotions when he was interviewed for this article at the end of August.​“Whenever I hear a love song, I get teary-eyed and sing along, because I’m so happy,” he said. “It’s so weird, because I felt so coldhearted before. Now I want to talk to him all the time. I’m constantly wanting to text him, to be with him anytime I can.

“I’m the happiest I’ve ever been with Diego,” said Mr. Garland, whose only other serious relationship was as a first-year student at Georgia Tech. “When you feel it, you feel it. I was the kind of person who used to overthink everything, especially with my college boyfriend. I was always asking myself, ‘Do I really love him?’ That’s the difference. I’m not overanalyzing this. I just felt a spark with him, and knew this was the guy. I know that I love him.”

But what, exactly, is happening to a person like Mr. Garland, who finds himself in the throes of something that has inspired or stumped the bards, from Ovid to Frank Ocean? Let’s go to the scientists.

“One thing going on in the brain in early love is that it’s a state of stress,” said Dr. Richard S. Schwartz, an associate professor of psychiatry at Harvard Medical School who has studied the biological aspects of love. “Cortisol, the major marker of stress, goes up. Serotonin, which is associated with states of well-being, goes down. Serotonin activity is also low in O.C.D., which fits with all the preoccupied thoughts you can’t get out of your mind in early love.”

“You have no idea how many clients we see who have that question: ‘Am I really in love or not?’” said Dr. Jacqueline Olds, a fellow associate professor of psychiatry at Harvard Medical School (who is married to Dr. Schwartz). “The more intellectualized and obsessional a client is, the more they’re worried.”

“There are a lot of clients who are obsessive and intellectualized, who are terrified of losing control in any area,” Dr. Olds said. “And so being in love makes them feel out of control.”

Case Study No. 2Andrew Simon, 28, a law student at Georgetown University, had no idea his life was about to go topsy-turvy when he sat down June 24 to a wedding rehearsal dinner in Portland, Ore.

But then a friend grabbed his phone and started swiping through the dating app Bumble while saying half-jokingly that Mr. Simon needed to find someone who could be his date the following day.

He matched with a woman named Shelby Neal, a 25-year-old marketing strategist for Twenty Four 7, a design firm in Portland. Mr. Simon and Ms. Neal didn’t end up going to the wedding together, but the two texted each other furiously throughout the ceremony.“Her language was so striking and vivid and powerful and real, but it also felt like language that I could engage with all day,” said Mr. Simon, who was born and raised in Portland. “And so I just couldn’t get enough of talking with her.”

They agreed to meet June 27, hours before Mr. Simon planned to meet a friend for dinner. And when they did meet, the conversation flowed as easily as the texts. They laughed a lot, although it was hard for Mr. Simon to recall what they were laughing about, exactly.When they said goodbye, Mr. Simon felt sad but also elated that “someone like this exists on this planet.” Ms. Neal, for her part, didn’t expect to hear from him again.A half-hour into his dinner commitment, Mr. Simon couldn’t take it anymore. He told his friend he couldn’t stay a minute longer. He said he had met someone, and she was incredible, and he absolutely had to see her again before he flew back home early the next morning.

Mr. Simon called her to see if she wanted to go out for ice cream.

“I asked myself: ‘Is this “The Notebook”?’” Ms. Neal said. “He was interesting and thoughtful and compassionate and funny and smart. And it felt too good to be true.”They went to the ice cream place Salt and Straw. They waited a half-hour in line, but somehow they didn’t mind. Then they wandered the streets. After a half-hour, a block away from the hospital where Mr. Simon was born, they kissed.

After he made it back to Washington, D.C., Mr. Simon and Ms. Neal talked or texted every day. One night Ms. Neal was out with friends when a group of young men approached. She should have been flattered or at least vaguely interested, she felt, but all she wanted to do was text with Mr. Simon.

He called her one morning not long after that. An actual phone call. He said he had something to tell her.

“I was going to wait until we were in person, because I thought that was more meaningful,” Mr. Simon said. “But every bone in my body was telling me I must share this with this person, and I couldn’t wait any longer.

“It was a feeling I had never felt before, this intense desire to tell someone that I love them,” he said. “So I told her, and she paused. And she said, ‘I love you, too.’ I think I was shaken by the whole ordeal. It felt really vulnerable and really real.”

They had fallen fast, without the luxury of being in each other’s company for an extended period of time. Ms. Neal visited Mr. Simon in Washington, and they were together again when he made a trip back to Portland, where he had already planned to see his family.After his law school graduation in December, Mr. Simon plans to return to Portland. Both he and Ms. Neal know the potential pitfalls of having the other in their everyday lives.“I’m not fearful or anxious, because I’m excited to be on the adventure,” Mr. Simon said. “I know that there are certain ways the adventure could end, but there are also certain ways the adventure could live on forever.”

A Kiss at the BellagioOn July 2, a month after their first date, Mr. Garland and Mr. Gasca were gazing at the fountains of the Bellagio in Las Vegas.

“I love you,” Mr. Gasca said.

Without hesitating, Mr. Garland replied, “I love you, too.”

They kissed.

Roughly a week after that, Mr. Garland asked Mr. Gasca to move in. Now they have begun charting a future, one that includes marriage and children.

“Before, I didn’t know what love was,” Mr. Garland said. “I’m not jaded, but I kind of had given up hope. I would go with a guy and be done with it. I let my head get in the way a lot. And in this case, I’m leading with my heart.”________________

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